The subject invention relates generally to a method of synthesizing a double metal cyanide (DMC) catalyst by combining an aqueous solution of a first metal salt with an aqueous solution of a second metal salt and with an aqueous solution of an alkali metal cyanide in a single step to synthesize the DMC catalyst. More specifically, the subject invention preferably combines an aqueous solution of ZnCl2, as the first metal salt, with an aqueous solution of CoCl2, as the second metal salt, and with an aqueous solution of KCN, as the alkali metal cyanide, to synthesize the DMC catalyst.
Polyether polyols are integral intermediate components utilized to manufacture a wide array of products, including polyurethanes. As such, the production of polyether polyols is critical. It is known in the art that polyether polyols are produced from the polymerization of epoxides, such as propylene oxide (PO) and ethylene oxide (EO). It is also known in the art that double metal cyanide (DMC) catalysts are effective catalysts for the polymerization of the epoxides. DMC catalysts produce polyether polyols having narrow molecular weight distributions as well as relatively low unsaturation.
In conventional methods, DMC catalysts are prepared by combining an aqueous solution of a metal salt and an aqueous solution of a complex metal cyanide salt. As a specific example, an aqueous solution of ZnCl2 (excess), as the metal salt, is combined with an aqueous solution of K3Co(CN)6, as the complex metal cyanide salt. This combination precipitates out the desired DMC catalyst, in this case specifically Zn3[Co(CN)6]2. Examples of such conventional methods are disclosed in U.S. Pat. Nos. 5,470,813 and 5,714,639. These conventional methods, in one form or another, utilize a complex metal cyanide salt. The complex metal cyanide salts are very expensive which limits the economic viability of utilizing DMC catalysts in the production of polyether polyols.
Thus, it would be desirable to provide a method of synthesizing DMC catalysts that does not utilize expensive complex metal cyanide salts as intermediates thereby improving the economic viability of DMC catalysts utilized in the production of polyether polyols.
According to the present invention, a method of synthesizing a double metal cyanide (DMC) catalyst is provided. As disclosed above, the method of the subject invention does not utilize complex metal cyanide salts to synthesize the DMC catalyst.
The method of the subject invention, in a single step, combines an aqueous solution of a first metal salt of the general formula M(X)n wherein M is selected from the group consisting of aluminum, zinc, and the transition metals; X is an anion selected from the group consisting of halides, hydroxides, sulfates, carbonates, cyanides, oxalates, thiocyanates, isocyanates, isothiocyanates, carboxylates, and nitrates; and n is a value from 1 to 3 satisfying the valency state of M with an aqueous solution of a second metal salt of the general formula N(Y)n wherein N is selected from the group consisting of the transition metals and the lanthanides; Y is an anion selected from the group consisting of halides, hydroxides, sulfates, carbonates, cyanides, oxalates, thiocyanates, isocyanates, isothiocyanates, carboxylates, and nitrates; and n is a value from 1 to 3 satisfying the valency state of N; and with an aqueous solution of an alkali metal cyanide, such as KCN, to synthesize the DMC catalyst. Thus, the DMC catalyst is produced independent of the complex metal cyanide salt.
In a preferred embodiment of the subject invention, the method combines an aqueous solution of a first metal salt having the same general formula as above wherein M is more specifically selected from the group consisting of Al(III) and Zn(II); X is an anion more specifically selected from the group consisting of halides; and n is a value from 1 to 3 satisfying the valency state of M with an aqueous solution of a second metal salt having the same general formula as above wherein N is more specifically selected from the group consisting of the Fe(II), Fe(III), Co(II), and Co(III); Y is an anion more specifically selected from the group consisting of halides; and n is a value from 1 to 3 satisfying the valency state of N; and with an aqueous solution of an alkali metal cyanide in a single step to synthesize the DMC catalyst.
Finally, in a further preferred embodiment of the subject invention, the method of synthesizing the DMC catalyst combines an aqueous solution of ZnCl2 with an aqueous solution of CoCl2 and with an aqueous solution of KCN in a single step. It is to be understood that in alternative embodiments of the subject invention ZnCl2 may be substituted with Zn(OAc)2, namely zinc acetate.
A method of synthesizing a double metal cyanide (DMC) catalyst is disclosed. More specifically, the method of the subject invention synthesizes the DMC catalyst by combining aqueous solutions of a first metal salt, a second metal salt, and an alkali metal cyanide in a single step to synthesize the catalyst.
An aqueous solution of the first metal salt is prepared. The aqueous solution of the first metal salt can range from 1 to 50 parts by weight of the first metal salt based on 100 parts by weight of the aqueous solution. Similarly, aqueous solutions of a second metal salt and an alkali metal cyanide are also prepared. These aqueous solutions can also range from 1 to 50 parts by weight of the second metal salt and the alkali metal cyanide, respectively, based on 100 parts by weight of the aqueous solution. Additionally, the aqueous solutions of the first metal salt, the second metal salt, and the alkali metal cyanide may include an organic activator as discussed below.
The first metal salt of the subject invention observes the general formula M(X)n. In this formula, it is to be understood that M is selected from the group consisting of aluminum, zinc, and the transition metals, X is an anion selected from the group consisting of halides, hydroxides, sulfates, carbonates, cyanides, oxalates, thiocyanates, isocyanates, isothiocyanates, carboxylates, and nitrates, and n is a value from 1 to 3 satisfying the valency state of M. In the preferred embodiment of the subject invention, M is selected from the group consisting of Al(III) and Zn(II), X is selected from the group consisting of halides, and n is a value from 1 to 3 satisfying the valency state of M. The first metal salt of the subject invention may also be Zn(OAc)2. Most preferably, the first metal salt of the subject invention is ZnCl2.
The second metal salt of the subject invention observes the general formula N(Y)n. In this formula, it is to be understood that N is selected from the group consisting of the transition metals and the lanthanides, Y is an anion selected from the group consisting of halides, hydroxides, sulfates, carbonates, cyanides, oxalates, thiocyanates, isocyanates, isothiocyanates, carboxylates, and nitrates, and n is a value from 1 to 3 satisfying the valency state of N. In the preferred embodiment of the subject invention, N is selected from the group consisting of the Fe(II), Fe(III), Co(II), and Co(III), Y is selected from the group consisting of halides, and n is a value from 1 to 3 satisfying the valency state of N. Most preferably, the second metal salt of the subject invention is CoCl2.
It is understood that Group IA alkali metals may be utilized for the alkali metal cyanide of the subject invention. Preferably, the alkali metal cyanide utilized is KCN. However, it is to be understood that other alkali metal cyanides, such as LiCN and NaCN, may be utilized without varying the scope of the subject invention.
In one embodiment, the method of the subject invention first combines the aqueous solution of M(X)n and the aqueous solution of N(Y)n to establish a first aqueous solution. The first aqueous solution, including the aqueous solutions of both the first metal salt, M(X)n, and the second metal salt, N(Y)n, is combined with the aqueous solution of the alkali metal cyanide, such as an aqueous solution of KCN, to form a combination product. Alternatively, all three aqueous solutions can be combined in a single step.
Next, the combination product is filtered to collect a residual product. The residual product is triturated with a water-soluble organic activator. More specifically, the water soluble organic activator is selected from the group consisting of ethanol, isopropyl alcohol, n-butyl alcohol, sec-butyl alcohol, tert-butyl alcohol, isobutyl alcohol, and mixtures thereof. Preferably, the water soluble organic activator is tert-butyl alcohol. Finally, the residual product is dried, preferably air-dried, thus isolating the DMC catalyst.
The following examples illustrate the nature of the subject method invention with regard to the synthesis of the DMC catalyst. The examples presented herein are intended to demonstrate the objects of the invention but should not be considered as limitations thereto.